WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (TWENTYSEVEN) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 127.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 350 NM EAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
DESPITE MOVING TOWARDS A DIURNAL MIN PHASE, TROPICAL STORM 27W IS
CONSOLIDATING AROUND THE LOW LEVEL CIRCULATION CENTER AND
CONVECTION IS DEEPENING, ESPECIALLY IN THE BANDING ALONG THE SOUTH
SIDE OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE VORTEX IS ALSO
TUCKING ITSELF FURTHER UNDERNEATH THE CONVECTION. THE INTENSITY IS
ASSESSED BASED ON THE JTWC DVORAK AND THE CIMSS ADT ESTIMATE OF
45KTS, AND THERE ARE INDICATIONS OF A DEVELOPING MICROWAVE EYE IN
012124Z GMI SERIES. THE SYSTEM IS TRACKING ALONG A STEADY
WEST-NORTHWESTERLY BEARING WHILE STEADILY DEEPENING. ANIMATED WATER
VAPOR IMAGERY AND TOTAL PRECIPITABLE WATER LOOPS VERIFY THAT THE
SYSTEM HAS COCOONED ITSELF AND WILL BE ABLE TO CARRY ITS MOISTURE
WITH IT TO THE LUZON COAST. THE ENVIRONMENT BETWEEN THE CURRENT
POSITION AND THE COAST IS CONSISTENT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE SOUTHERN FLANK OF THE SUBTROPICAL
RIDGE, WHICH IS ANCHORED IN A MID-LEVEL ANTICYCLONE CENTERED JUST
NORTHEAST OF TAIWAN. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS SATCON: 40 KTS AT 1930Z
   CIMSS ADT: 45 KTS AT 0100Z
   CIMSS AIDT: 41 KTS AT 0220Z
   CIMSS D-PRINT: 39 KTS AT 020000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: A STEADY AND STATIONARY SUBTROPICAL RIDGE
EXTENDING OVER THE REGION WILL DRIVE THE SYSTEM ALONG A STEADY
WEST-NORTHWEST BEARING TO A LANDFALL BETWEEN PALANAN AND CASIGURAN.  
THE FAVORABLE ENVIRONMENT WILL ALLOW THE SYSTEM TO RAMP LOW TYPHOON 
STRENGTH PRIOR TO LANDFALL. THE RUGGED TERRAIN OF NORTHERN LUZON WILL 
TEAR THE SYSTEM UP AND MAKE IT DIFFICULT TO TRACK UNTIL IT TRACKS 
OFF-SHORE SOMEWHERE NEAR VIGAN AND REGATHERS ITSELF OVER THE WEST 
PHILIPPINE SEA. THE ENVIRONMENT BETWEEN LUZON AND HAINAN IS ALSO VERY
FAVORABLE, WITH ANOTHER STRETCH OF LOW VERTICAL WIND SHEAR AND
PLENTY OF DEEP MOISTURE OVER THE SOUTHERN PORTION OF THE STORM TO
ALLOW IT TO DEEPEN TO TYPHOON STRENGTH BEFORE APPROACHING COASTAL
CHINA. 


MODEL DISCUSSION: TRACK GUIDANCE IS TIGHT AND THE JTWC FORECAST
STAYS BETWEEN THE MULTI-MODEL CONSENSUS AND THE ECMWF ENSEMBLE MEAN
AND A NEW AI-DERIVED TRACKER. FOR THE MOST PART, INTENSITY GUIDANCE
DOES NOT HANDLE THE TRIP OVER LUZON, BUT HAFS-A SHOWS A GOOD
SENSITIVITY TO THAT LEG. IT DOES, HOWEVER, TRACK THE SYSTEM ACROSS
LUZON AT 55KTS. THE MOST DIFFICULT POINTS OF THE FORECAST INVOLVING
ESTIMATING THE AMOUNT OF DECAY THE SYSTEM UNDERGOES AS IT TRACKS
OVER LUZON, AND HOW QUICKLY IT REGATHERS ITSELF ONCE IT MOVES INTO
THE WEST PHILIPPINE SEA. THE JTWC INTENSITY FORECAST FOLLOWS THE
HAFS-A TREND, ALTHOUGH IT DECAYS THE STORM MORE THAN THE MODEL
INDICATES. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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